What is Solar Eclipse:
An eclipse is a natural phenomenon. We all knows about it more or less, even though what branch we belongs from.But being a student of physics generally i wish to make you know some thing more. Its not about countless equation but about a outline of the system. Most probably we all know recently on 21st august there was an solar eclipse which was visible within a band across the entire contiguous united states, passing from pacific to Atlantic Coasts. Today i am going to express some thing related on this topic.
In ancient days solar eclipse were regarded as bad omens. In that time people related it with their supertitious belief as Sun seems to disappear during the day and the sky darkens in a matter of minute. Even in modern culture few still cannot accept it as scientific cause. They still attribute it as supernatural cause and unaware of its astronomical explanations.
What actually happens:
A solar eclipse is a type of eclipse that occurs when the moon passes between the Sun and Earth and when it partially or entirely block the sun. In a total eclipse the disk of the sun is fully obscured by the Moon whereas in partial, only part of the sun is obscured. Since the moon’s orbit is tilted at more than 5 degree to the earth’s orbit around the sun, its shadow usually misses earth. The moon’s orbit must cross earth’s ecliptic plane in order for an eclipse to occur. In addition, the moon’s actual orbit is elliptical, often taking it far away from earth that its apparent size is not large enough to block the sun entirely. The orbital planes cross each other at a line of nodes resulting in at least two, and up to five, in each year. But eventually no more than two of which can be seen as total eclipses. However total solar eclipses are rare.
Types of solar eclipse:
In general,four types of solar eclipses are there:
1. A Total Eclipse
A total eclipse occurs when the dark silhouette of the moon completely block the intensely bright light of the sun.It allows the fainter solar corona to be visible.During any one eclipse,totality occurs at best only in a narrow track on the surface of earth.
2. An Annular Eclipse
An annular eclipse occurs when the sun and moon are exactly in line with the earth,but the apparent size of moon is smaller then that of sun.Hence sun appears as a very bright ring,surrounding the dark disk of the moon
3. A Hybrid Eclipse
It shifts between a total and annular eclipse.At certain points on the earth surface it appears as total whereas at other point it seems be an annular eclipse.Comparatively these are rare.
4. A partial eclipse
It appears when the sun and moon are not exactly in line with the earth and moon partially abscures the sun.This can usually be seen from a large part of earth.But partial eclipse are virtually unnoticeable in terms of the sun brightness.Of course it can be observed through a darkening filter which should always be used for safety.
A separate category of solar eclipse is that of the sun being occluded by a body other than moon,as can be observed at points in space away from earth’s surface.
Science behind the Event:
The moon’s orbit around the earth is slightly elliptical,as is the earth’s orbit around the sun.The apparent size of the sun and moon therefore vary.The moon distance about the earth can vary by 6% from average value.Therefore moon’s apparent size varies with its distance from earth and its effect leads to difference between total and annual eclipses.The majority of central eclipse are annular as generally moon goes to far from earth in average.Only when it comes closer than average distance to earth, the total eclipse occurs and from the region of earth in which umbra(the dark gray region between the moon and earth)touches,solar eclipse can be seen.The larger light gray area is the penumbra,in which partial eclipse can be viewed. The magnitude of an eclipse is the ratio of the apparent size of moon to the apparent size of sun.when moon comes closer to earth the magnitude goes to greater or equal to 1000 whereas when moon is near its farthest distance to earth the magnitude becomes less than one.
A hybrid eclipse occurs when the magnitude of an eclipse changes during the event from less to greater than one,these eclipses are extremely narrow in their path width and extremely short in their duration at any point,at most just a few seconds at any location within just a few kms of the centreline of the path.
Now the phase observed during a total solar eclipse are first contact,second contact,totality,third contact,fourth contact.
How to visualize a Solar Eclipse:
since looking directly at the sun can lead to permanent eye damage,special eye protection are used when viewing a solar eclipse.It is only safe to view only the total phase of a total solar eclipse with unaided eye which can only last a maximum of 7.5 minutes but most people are not trained to recognize the phases of an eclipse.
Finally i have to tell that we are fortunate to have opportunity like this to see solar eclipses whether total or partial.These are seen on earth because of a fortuitous combination of circumstances.This is an excellent and surprising phenomenon that sun earth moon comes in a straight line in universe after having different path with different anguar diameter.Thousands of years ago the moon was enough closer to earth, so all the eclipses were total.Due to tidal acceleration, the orbit of moon around earth increases 3.8 cm each year.Hence it is estimated when the moon will be unable to occlude the entire sun viewed from earth ranges between 1.4 billion and 650 million years in future.
For more information you may visit https://eclipse.gsfc.nasa.gov/solar.html